x86, boot: add free_early to early reservation machanism

Add free_early to early reservation mechanism - this way early bootup
failure paths can stop wasting memory.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>